A flash memory device includes a memory device that may retain written data despite an abrupt power interruption. A metal oxide semiconductor (MOS) transistor of a flash memory device may include a floating gate, which can accumulate an electric charge. In the flash memory device, a thin gate oxide layer, such as a tunnel insulating layer, can be disposed on a semiconductor substrate. The floating gate, which can be formed of a conductive material, can be disposed on the gate oxide layer. A control gate can be disposed over the floating gate by interposing an inter-gate dielectric layer between the control gate and the floating gate. Accordingly, the floating gate can be electrically insulated from the semiconductor substrate and the control gate by the tunnel insulating layer and the inter-gate dielectric layer. The inter-gate dielectric layer may include an oxide-nitride-oxide (ONO) structure, for example, a SiO2/Si3N4/SiO2 structure.
However, since the inter-gate dielectric layer including the ONO structure may have a low dielectric constant, there may be a limitation in lowering the equivalent oxide thickness (EOT). In order to address the low dielectric constant of the ONO dielectric layer, a metal oxide layer having a dielectric constant of 8 or higher may be used as the inter-gate dielectric layer. The dielectric constants and energy bandgaps of SiO2, Si3N4, and other metal oxides are shown below in Table 1.
TABLE 1Inter-gate Dielectric LayerDielectric ConstantEnergy bandgap(eV)SiO23.98.9Si3N475.1Al2O398.7ZrO235~405.5~5.8
As can be seen from Table 1, SiO2, which can be applied to the ONO dielectric layer, may have a dielectric constant of 3.9 and an energy bandgap of 8.9 eV, and Si3N4, which can also be applied to the ONO dielectric layer, may have a dielectric constant of 7 and an energy bandgap of 5.1 eV. Because the ONO dielectric layer may have a relatively low dielectric constant, it may not meet the conditions of high integration density. In other words, it may be problematic to reduce the thickness of the ONO inter-gate dielectric layer due, at least in part, to its low dielectric constant so that the inter-gate dielectric layer may not be readily applied to a high-speed/high-integrated device.
An aluminum oxide (Al2O3) layer may have a suitable energy bandgap of 8.7 eV, but its dielectric constant of around 8 may be too low to affect the EOT. A zirconium oxide (ZrO2) layer may exhibit a higher dielectric constant of 35 to 40, which may be sufficient to lower the EOT, but may have a lower bandgap of 5.5 to 5.8 eV, and thus, leakage current characteristics may decline. Therefore, a dielectric layer including a combination of zirconium oxide and aluminum oxide may be formed in order to address some of the disadvantages associated with using either oxide alone.
A method of forming a dielectric layer by stacking the zirconium oxide layer and the aluminum oxide layer is discussed in U.S. Pat. No. 6,660,660 entitled “Methods for Making a Dielectric Stack in an Integrated Circuit.” According to U.S. Pat. No. 6,660,660, a zirconium oxide layer and an aluminum oxide layer are formed by an atomic layer deposition (ALD) process. The zirconium oxide layer is formed using ZrCl4 and H2O as a source gas and a reactive gas, respectively, and the aluminum oxide layer is formed using TMA(trimethyl aluminum; Al(CH3)3) and H2O as a source gas and a reactive gas, respectively. However, when the zirconium oxide layer and the aluminum oxide layer are formed using H2O as a reactive gas, they may contain —OH radicals. As a result, the dielectric layer may be degraded due to the chemical properties of —OH radicals.
Furthermore, when two or more material layers are formed by the ALD process, the ZrCl4 and TMA source gases may be transferred and sprayed through respective gas supply lines configured to provide the source gas to a shower head mounted in a chamber. In this case, it may be cost-effective for the source gases to be transferred and sprayed at similar temperatures. However, the ZrCl4 source gas is usually transferred at a temperature of about 180 to 200° C., while the TMA source gas is usually transferred at a temperature of about 20 to 130° C. For example, if the TMA source gas is transferred through a gas supply line that is configured to contain a gas and maintain the temperature of the gas within the gas supply line at a temperature of higher than about 130° C., the TMA source gas may decompose in the gas supply line before it is sprayed into the chamber. Thus, the TMA source may not retain its chemical properties. To reduce the occurrence of this phenomenon, the temperatures within the gas supply lines may be separately controlled in one shower head. However, it may be difficult to separately control the temperatures of the gas lines, and such issues related to temperature control may result in decreased efficiency of the manufacturing process.